Agronomic efficiency of nitrogen fertilizers for wheat

Abstract

Urea is the most used nitrogen (N) fertilizer in Brazil. PETROFÉRTIL Company aggregated to urea and to other N fertilizers, gypsum, ammonium sulphate, and Patos rock phosphate. In order to test these fertilizers, three experiments were carried out with wheat, using microplots (1984) and conventionally sized field plots (1987 and 1988). The soil was a Dark-Red Latosol (Haplohumox), presenting 4.5% (microplots) and 2.8% (conventional plots) of organic matter. Based on N absorption by wheat in the microplots, the following fertilizers presented values equal or above 100% agronomic efficiency (AE), using ammonium nitrate as reference source: nitrosulfocalcium gypsum DH (113%), nitrocalcium (109%), urea covered with gypsum (106%), urea nitrate compacted with Patos rock phosphate (105%), nitromagsulfocalcium gypsum HH (105%), and urea compacted with ammonium sulphate (100%). Seven sources were selected from this experiment and used in the next two trials, carried out under conventional plots. In 1987 there were no significant differences in yield and only small differences in AE among N sources were observed. In 1988 significant grain yield differences were obtained among N fertilizers, being urea statistically equivalent to the following products: urea nitrate compacted with Patos rock phoshate, urea covered with gypsum, urea covered with ammonium sulphate, and nitrocalcium. The AE of urea in this trial was 126%. It was concluded that the aggregation of various compounds to urea did not increase steadily its AE for wheat.